An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri - Paris Observatory

1) The backward counting in fixed time units from the initiation of a
project, as a rocket launching, with the moment of firing designated as
zero.
2) The final preparations made during this period (Dictionary.com).

A scenario of galaxy formation whereby massive galaxies formed earlier
in the history of the → Universe (i.e. at high
→ redshifts) and completed their
→ star formation process more rapidly
than low-mass galaxies. This scenario contrasts with what might be expected from simple
→ hierarchical structure formation scenarios,
which predict that large galaxies formed in more recent times through the
→ merging of small galaxies.

Downsizing, first suggested by Cowie et al. (1996, AJ 112, 839), from
downsize (v.), is a new sense for this term. Its current main meaning
in non astrophysical contexts is "to make in a smaller size, or become
smaller in size (in particular in economic vocabulary, by reductions in
personnel)," from → down + → size.

A severe accident in a nuclear reactor which is caused by a major failure in
the reactor cooling circuit leading to the melting of the reactor core.
Without coolant, the core would overheat so that the uranium fuel would melt. If the core
continued to heat up, the steel walls of the core would also melt. If the molten
core escaped from the containment housing of the reactor, large amounts of highly
radioactive materials would be released into the atmosphere. The radioactive
contamination of the air, water, and soil can have disastrous consequences for life.

The last stage of → merger between two
→ black holes undergoing → inspiral.
At the end of the evolution of a → binary black hole
system, the black holes get close enough to → merge
together into a single, larger black hole (→ black hole merger).
The resulting black hole is at first
distorted and asymmetric, but in the ringdown process
the black hole's vibrations decay due to → gravitational radiation
leaving finally a quiescent, spinning black hole.

In computer science, to reduce the processing power of the same node/system
by reducing its resources (CPU, RAM, etc.).
This type of → vertical scaling is opposite to
→ scale up. See also → scale in,
→ scale out.

A phenomenon in which the rotation period of a pulsar steadily decreases with the pulsar
age. The cause of the spin-down is magnetic torque due to the strong fields threading out
from the pulsar. The magnetic energy is being converted to high-energy particles
and radiation from the nebula. Observed spin-down rates range from about
10-5 seconds/year for the
youngest pulsars to about 10-12 seconds/year for recycled pulsars. The Crab pulsar
is slowing down at a rate of about 10-5 seconds/year.
Knowing the rotation period and the lengthening rate of a pulsar leads
to its age.